An Analysis Of Secondary Circulations And Their Effects Caused By Small-Scale Surface Inhomogeneities Using Large-Eddy Simulation

A parallelized large-eddy simulation model has been used to investigate the effects of two-dimensional, discontinuous, small-scale surface heterogeneities on the turbulence structure of the convective boundary layer.Heterogeneities had a typical size of about the boundary-layer heightz_i. They were produced by a surface sensible heat flux pattern ofchessboard-type and of strong amplitude as typical, e.g., for the marginalice zone. The major objectives of this study were to determinethe effects of such strong amplitude heat flux variations and to specify theinfluence of different speeds and directions of the background wind.Special emphasis has been given to investigate the secondary circulations induced by the heterogeneities by means of three-dimensional phase averages.Compared with earlier studies of continuous inhomogeneities, the same sizeddiscontinuous inhomogeneities in this study show similar but stronger effects.Significant changes compared with uniform surface heating are only observedwhen the scale of the inhomogeneities is increased to z_i. Especially the vertical energy transport is much more vigorous and even the mean emperature profile shows a positive lapse rate within the whole mixed layer. However, the effects are not directly caused by the different shape of the inhomogeneities but can mainly be attributed to the large amplitude of the imposed heat flux,as it is typical for the partially ice covered sea during cold air outbreaks.The structure of the secondary flow is found to be very sensitive to the wavelength and shape of the inhomogeneities as well as to the heatflux amplitude, wind speed and wind direction. The main controlling parameter is the near-surface temperature distribution and the related horizontal pressure gradient perpendicular to the main flow direction. The secondary flow varies from a direct circulation with updraughts mainly above the centre of the heated regions to a more indirect circulation with updraughts beneath the centre and downdraughts above it. For background winds larger than 2.5 m s^–1 a roll-like circulation pattern is observed.From previous findings it has often been stated that moderate backgroundwinds of 5 m s^–1 eliminate all impacts of surface inhomogeneitiesthat could potentially be produced in realistic landscapes. However, this studyshows that the effects caused by increasing the wind speed stronglydepend on the wind direction relative to the orientation of theinhomogeneities. Secondary circulations remain strong, even for abackground wind of 7.5 m s^–1, when the wind direction is orientatedalong one of the two diagonals of the chessboard pattern. On the otherhand, the effects of inhomogeneities are considerably reduced, even undera modest background wind of 2.5 m s^–1, if the wind direction isturned by 45°. Mechanisms for the different flow regimesare discussed.     

斯堪的那维亚臭氧亏损和地面加热

对ＮＡＳＡ的ＴＯＭＳ臭氧资料进行分析后指出：冬季在北极的斯堪的那维亚地区存在一个明显的臭氧亏损区，亏损区的中心值达－５０ ＤＵ，相当于该区域平均值的 １５％。对臭氧亏损和北大西洋海温的东西向差异作相关分析得到：其季节变化的相关系数为－０．９６，逐月（ １６８个月）变化的相关系数为－０．７０。同样对臭氧亏损与地面加热进行相关分析后指出：斯堪的那维亚地区的臭氧亏损和该地区地面的热通量关系极其密切，其相关系数均在－０．８７以上。由此我们认为：北大西洋暖流向北输送能量，引起斯堪的纳维亚地区地面加热，由此造成了冬季该地区的臭氧亏损。     

南海海平面高度年循环的特征

根据 ＴＯＰＥＸ／ ＰＯＳＥＩＤＯＮ－ＥＲＳ高度计提供的海平面高度异常资料和并行海洋气候模式（ＰＯＣＭ）模拟海平面高度资料，分析了南海海平面高度年循环特征。结果表明：ｌ月，３月和５月海平面高度的异常值分别与７月，９月，１１月的异常值相反。ｌ月（７月），深水海区与吕宋海峡的海平面高度为负（正）异常，在大部分陆架区和南海的西和南部，海平面高度为正（负）异常。在３月（９月），除海平面高度异常的量级已减少，且较小的ＳＳＨ正异常（负异常）出现在南海的中部以外，海平面高度异常的分布型与 １月（７月）类似； ＳＳＨ的年循环的最大振幅出现在吕宋岛的西北海域；风的季节变化是南海ＳＳＨ季节变化的主要原因。     

近地表低速带参数反演

阐明利用瑞雷面波反地表速度和厚度的可行性，并利用地震记录中的瑞雷面波数据，反演近地表低速带的厚度和速度，文中给出了实例试算，结果表明，面波资料的近地表参数反演将有利于勘探目标区的物理参数建模。     

近地表Q值求取及振幅补偿

利用面波衰减的Q模型，反演出近地表的Q值，据此，给出消除振幅受近地表影响的振幅静校正，利用时间剩余校正方法解决了振幅问题，实际计算结果表明本文方法能有效地去除振幅异常。     

利用卫星资料试作青藏高原地表净辐射场的气候反演

利用 ERBE和 ISCCP卫星辐射及总云量资料 ,结合已提出的地表短波吸收辐射 ,大气逆辐射以及地表长波辐射的气候反演方法 ,计算出 2 5°～ 4 0°N,75°～ 95°E间 2 .5°× 2 .5°经纬度网络点及高原 63个站点的各月平均地表净辐射 ,绘制出其在高原的分布图 ,揭示其时空分布特征。     

2001年11月14日青新交界MS8.1地震地表破裂带的初步调查

初步的野外调查表明,2001年11月14日青新交界8.1级地震的地表破裂带位于昆仑山南麓,西端可能终止于布喀达坂峰,东端点距青藏公路以东70km.主破裂带总长度可达350km,总体走向N80°～85°W.具明显的左旋水平走滑运动性质,最大左错量为6m.宏观震中初步定在库赛湖东约30km一带,震中区烈度定为Ⅺ度根据初定宏观震中的位置,建议将该地震命名为库赛湖地震.     

厄尔尼诺与亚洲季风对港澳地区降雨影响

分析研究了香港1853～1997年（145年）、澳门1901～1997年（97年）的月和年降雨量的一些特征。主要结论是：（1）香港、澳门年降雨量存在准2～6年的周期振荡，澳门年降雨量有很强的长期趋势，香港年降雨量无明显趋势；（2）香港、澳门年内雨量的峰值出现在西南季风期（6月和8月），而谷值在东北季风期（12月）；（3）EI Nino事件年，香港、澳门年降雨量距平百分率多为正，降雨偏多。在La Nila事件年，香港、澳门年降雨量距平百分率多为负，降雨偏少。     

Simple formulations of ground impedance functions for rigid surface foundations

A differential equation is formulated for the dynamic response of ground medium by using a simplified ground model. Applying Galerkin's procedure for weighted residual, this equation leads to a governing equation only at the ground surface. The equation indicates that the ground surface behavior can be computed even further by a simplified model. By solving the governing equation for the boundary conditions along the surface, expressions in simple closed forms are developed for the dynamic response analysis of a massless rigid foundation that rests on the ground surface. Despite their significant simplicity, the developed expressions compute the values very close to those computed by far more complex rigorous solutions. They are found to be capable of capturing the important characteristics of the dynamic ground behavior well.     

River flow mass exponents with fractal channel networks and rainfall

An important problem in hydrologic science is understanding how river flow is influenced by rainfall properties and drainage basin characteristics. In this paper we consider one approach, the use of mass exponents, in examining the relation of river flow to rainfall and the channel network, which provides the primary conduit for transport of water to the outlet in a large basin. Mass exponents, which characterize the power-law behavior of moments as a function of scale, are ideally suited for defining scaling behavior of processes that exhibit a high degree of variability or intermittency. The main result in this paper is an expression relating the mass exponent of flow resulting from an instantaneous burst of rainfall to the mass exponents of spatial rainfall and that of the network width function. Spatial rainfall is modeled as a random multiplicative cascade and the channel network as a recursive replacement tree; these fractal models reproduce certain types of self-similar behavior seen in actual rainfall and networks. It is shown that under these modeling assumptions the scaling behavior of flow mirrors that of rainfall if rainfall is highly variable in space, and on the other hand flow mirrors the structure of the network if rainfall is not so highly variable.